North Korea has "clarified its resolute stand that it would take countermeasures including nuclear test to protect the sovereignty and dignity of the" country, the North's official Korean Central News Agency reported, citing the ruling party's Rodong Sinmun newspaper.
The Institute for Science and International Security think tank said in a report Saturday that satellite imagery from Friday showed ongoing activities at North Korea's nuclear test site, including movement of possible vehicles, trucks and containers. The think tank said the exact timing of a test was difficult to tell.
On Thursday, South Korean Defence Minister Kim Kwan-jin said that North Korea was making final preparations to conduct its fourth nuclear test. Kim, however, said it could be a bluff and did not elaborate on what the final step of the North's preparations would be. Seoul has warned that Pyongyang would face serious consequences if it conducts a nuclear test.
A fourth test would mark another defiant response to United States-led international pressure on North Korea to abandon its nuclear weapons program. The North conducted nuclear tests in 2006, 2009 and 2013.
Recent months have seen animosities flare up on the Korean Peninsula, with Pyongyang conducting a barrage of rocket and missile tests and resuming fierce rhetoric against Seoul and Washington.
In late March, in a show of defiance to the United Nations Security Council's denouncing of Pyongyang's rocket-launching drills, North Korea's Foreign Ministry said the country was "fully ready for next-stage steps which the enemy can hardly imagine" and that "it would not rule out a new form of nuclear test for bolstering up its nuclear deterrence."
The two Koreas have been divided along the world's most heavily armed border since the 1950 to 1953 Korean War ended with an armistice, not a peace treaty.